There has been known such a technique capable of allowing a storage battery to supply power to a power grid and an electric load (see for example, JP 2000-224769 A (hereinafter, referred to as “Document 1”)). Document 1 mentions that a person of the customer facility buys power at a late-night rate to charge the storage battery and sells charged power to a power company at a daytime rate and thereby can earn income corresponding to a difference between the rates. Further, Document 1 mentions that supply of power from the storage battery to the power grid by the person of the customer facility can offer various benefits such as load leveling, responding to a sharp demand fluctuation, and improved power quality of a distribution line. Additionally, Document 1 mentions that the power company may give rewards for some of the benefits, to the person of the customer facility.
Document 1 mentions that the person of the customer facility can perform charging and discharging of the storage battery in the customer facility to provide benefits to the power company. However, benefits for the person of the customer facility disclosed in Document 1 are income corresponding to the difference between the power rates in charging and discharging, and the rewards for the benefits obtained by the power company. Document 1 does not give any teachings for further motivating the person of the customer facility to increase a profit thereof.